1. Field of the Invention
The present invention relates to a recording/reproducing apparatus such as an optical disk and, more particularly, to a recording/reproducing apparatus in which a track skip caused by scratches in a disk is suppressed.
2. Description of the Related Art
In a recording/reproducing apparatus such as an optical disk apparatus, when a scratch is in the disk, a process such as a process of holding a tracking servo operation to assure of the stability of the tracking servo operation is performed after the scratch is detected by an RF signal. A conventional recording/reproducing apparatus will be described below with reference to FIGS. 3 and 4 by using an optical disk apparatus as an example.
FIG. 3 is a block diagram showing a main part of the optical disk apparatus, and FIG. 4 is a timing chart for explaining operations in detection of a scratch. As shown in FIG. 3, in the optical disk apparatus, an optical disk (to be referred to as a disk hereinafter) 2 rotated by a spindle motor 1, an optical head (to be referred to as a head hereinafter) 4 for performing track tracing of an optical beam with movement of a lens 3 or the like with respect to the track of the disk 2, and a servo processor 5 for controlling the head 4 or the like according to a track error signal (TE signal) indicating a track position error of the head 4 or a reproduced RF signal are arranged. The servo processor 5 is constituted by a scratch detection circuit 6 serving as a scratch detection means for detecting a scratch in the disk on the basis of the RF signal, a tracking servo equalizer 7 for controlling the lens 3 and the head 4 on the basis of the tracking error signal, and a coarse movement supply servo equalizer 8. The tracking servo equalizer 7 outputs the track servo signal to an actuator driver 9 according to a tracking error signal TE, so that the actuator driver 9 controls the lens 3 or the like of the head 4.
Signals are recorded on a track spirally formed on the disk 2 from the inner periphery to the outer periphery, and an optical beam is irradiated on the track. A movable range of the optical beam irradiated on the disk 2 in the track direction is the range of about several tens tracks in only a tracking servo operation of the lens 3, and the entire surface of the disk 2 cannot be accessed. For this reason, the head 4 must be moved, and a coarse movement motor 10 serving as a moving means is used. As the coarse movement motor 10, a stepping motor is generally used. In movement between tracks whose range exceeds the limited range of tracking servo, a coarse movement control signal from the coarse movement supply servo equalizer 8 operating in response to a tracking error signal TE is output to the coarse movement motor driver 12 through a switching circuit 11. Although a reference voltage from a reference signal generation circuit 13 is also input to the switching circuit 11, a coarse movement control signal from the coarse movement supply servo equalizer 8 is generally input to a coarse movement motor driver 12 to rotatably drive the coarse movement motor 10, thereby moving the head 4.
When the disk 2 has a scratch such as a defect formed thereon, a reflected beam is offset from a spot (not shown) for detecting a tracking error, the tracking error signal TE cannot be detected, and a tracking servo operation is disabled, so that a track skip occurs. As a countermeasure against the track skip, a scratch detection signal from the scratch detection circuit 6 is input to the switching circuit 11. When the disk 2 has a scratch or the like formed thereon, a lack of a reproduced RF signal occurs. For this reason, the scratch or the like is detected by the scratch detection circuit 6, and a detected scratch detection signal switches the switching circuit 11, so that a reference voltage from the reference signal generation circuit 13 is input to the coarse movement motor driver 12 in place of a coarse control signal from the coarse movement supply servo equalizer 8. This operation is a coarse movement stop operation. In this manner, the stability of a tracking servo operation is realized.
The above operation will be described below with reference to FIG. 4. When the disk has a scratch, a notched portion D appears between t1 and t2 in a reproduced RF signal as shown in FIG. 4A. The scratch detection circuit 6 detects the scratch on the basis of the notched portion D, and, as shown in FIG. 4B, the scratch detection circuit 6 outputs a scratch detection signal S to the switching circuit 11 between t3 and t4 a predetermined period of time after t1. On the other hand, since a reflected beam from a spot for detecting a tracking error is eliminated due to the scratch, tracking servo acts to gradually increase the tracking error signal from t1 to t3 as shown in FIG. 4C. In this state, a light beam jumps over many tracks. For this reason, the switching circuit 11 is switched by a scratch detection signal S from the scratch detection circuit 6 to hold tracking servo between t3 and t4, and a reference voltage from the reference signal generation circuit 13 is input to the coarse movement motor driver 12 in place of a coarse control signal from the coarse movement supply servo equalizer 8. Since the coarse movement motor driver 12 has a reference voltage having the same value as that of the reference signal generation circuit 13, the coarse movement motor driver 12 does not output a rotatable drive power to the coarse movement motor 10. Therefore, drive rotation of the coarse movement motor 10 is stopped.
Although the coarse movement stop is effective between time t3 and time t4 between which the scratch detection circuit 6 detects a scratch to output a scratch detection signal S, the coarse movement stop is not effected in a period of time (from time t1 to time t3) until the detection of scratch and a period of time (from t4 to t2) after the detection of scratch. For this reason, the level of a tracking error signal is high. Therefore, the coarse movement supply servo equalizer 8 acts to generate relatively large vibrations Q1 and Q2 near t3 and t4. These vibrations are input to the coarse movement motor driver 12, and the coarse movement motor 10 is rotatably driven to move the head 4.
In the conventional recording/reproducing apparatus, with respect to a scratch in the disk, tracking servo is held after a defective signal is detected. However, since a coarse movement stop mechanism is interlocked with the tracking servo, a coarse movement stop operation is also performed after the scratch is detected. For this reason, vibration is generated when the head passes through the scratch, and the vibration is given to the head to easily cause a track skip (off track) to occur.